ENVIRONMENTAL SCIENCE 14th Edition A Study of Interrelationships

Outline 5.1 Ecological Concepts 5.2 The Role of Natural Selection and Evolution 5.3 Kinds of Organism Interactions 5.4 Community and Ecosystem Interactions

5.1 Ecological Concepts Ecology is the study of ways organisms interact with each other and with their nonliving surroundings. Environment means everything that affects an organism during its lifetime. Abiotic factors: Nonliving things that influence an organism, such as energy, nonliving matter, living space, and ecological processes. Biotic factors: All forms of life with which the organism interacts.

Levels of Organization in Ecology

Limiting Factors Limiting factors are any factors whose shortage or absence restricts species success. Scarcity of water or specific nutrients (plants). Climate, availability of a specific food (animals). Range of tolerance indicates a range of conditions in which an organism can survive. Some species have a broad range of tolerance, while others have a narrow range of tolerance.

Temperature Is a Limiting Factor

Habitat and Niche The habitat of an organism is the space in which an organism lives; it is defined by the biological requirements of each particular organism. Usually highlighted by prominent physical or biological features. The niche of an organism is the functional role (profession) the organism has in its surroundings. This term includes all the ways an organism affects the organisms with which it interacts as well as how it modifies its physical surroundings.

Moss Habitat

Habitat and Niche The Niche of a Dandelion The Ecological Niche of a Beaver The Niche of a Dandelion

Genes, Populations, and Species Genes are distinct pieces of DNA that determine the characteristics an individual displays. A population includes all organisms of the same kind found within a specific geographic region. A population contains more kinds of genes than any single individual within the population. A species is a population of all the organisms potentially capable of reproducing naturally among themselves and having offspring that also reproduce.

5.2 The Role of Natural Selection and Evolution Natural selection is the process that determines which individuals within a species will reproduce and pass their genes to the next generation. The changes seen in the genes and characteristics displayed by successive generations of a population of organisms over time is known as evolution.

Natural Selection Several conditions and steps are involved in the process of natural selection: Individuals within a species show genetically determined variation. Organisms within a species typically produce more offspring than are needed to replace the parents when they die. Most of the offspring die. The excess number of individuals results in a shortage of specific resources.

Natural Selection Due to individual variation, some individuals have a greater chance of obtaining needed resources and therefore have a greater likelihood of surviving and reproducing than others. As time passes, the percentage of individuals showing favorable variations will increase while the percentage showing unfavorable variations will decrease.

Evolutionary Patterns Speciation is the production of new species from previously existing species. It is thought to occur as a result of a species dividing into two isolated subpopulations. Extinction is the loss of an entire species. Of the estimated 500 million species believed to have ever existed on Earth, 98-99% have gone extinct. Coevolution is the concept that two or more species can reciprocally influence the evolutionary direction of the other. Grazing animals and grass species.

Change Resulting from Natural Selection

Evolutionary Patterns Speciation Extinction

Coevolution Coevolution is the concept that two or more species of organisms can reciprocally influence the evolutionary direction of the other. In other words, organisms affect the evolution of other organisms. Since all organisms are influenced by other organisms, this is a common pattern.

5.3 Kinds of Organism Interactions Predation is a kind of interaction in which one animal kills/eats another. Predator benefits from food. Prey adaptation is manifested in a higher reproduction rate.

Competition Competition is a kind of interaction in which two organisms strive to obtain the same limited resource. Intraspecific competition is competition between members of same species. Interspecific competition is competition between members of different species.

Competition The competitive exclusion principle holds that no two species can occupy the same ecological niche in the same place at the same time. Less-fit species must evolve into a slightly different niche.

Niche Specialization

Symbiotic Relationships Symbiosis is a close, long-lasting, physical relationship between two different species. At least one species derives benefit from the interaction. There are three categories of symbiotic relationships: Parasitism Commensalism Mutualism

Symbiotic Relationships Commensalism is a relationship in which one organism benefits while the other is not affected. Remoras and sharks Mutualism is a relationship in which both species benefit. The relationship is obligatory in many cases, as neither can exist without the other. Mycorrhizae

Symbiotic Relationships Parasitism is a relationship in which one organism (parasite) lives in or on another organism (host), from which it derives nourishment. Ectoparasites live on the host’s surface. Fleas, lice, molds, mildews Endoparasites live inside the body of the host. Tapeworms, malaria parasites, bacteria, fungi

Parasitism

Commensalism

Mutualism Oxpeckers removing parasites Root nodules containing nitrogen-fixing bacteria Oxpeckers removing parasites

5.4 Community and Ecosystem Interactions A community is an assemblage of all interacting species of organisms in an area. An ecosystem is a defined space in which interactions take place between a community, with all its complex interrelationships, and the physical environment.

Major Roles of Organisms in Ecosystems Ecologists have divided organisms’ roles in ecosystems into three broad categories: Producers: Organisms that are able to use sources of energy to make complex organic molecules from simple inorganic substances in their environment. Consumers are organisms that require organic matter as a source of food. Decomposers are organisms that use nonliving organic matter as a source of energy and raw materials to build their bodies.

Major Roles of Organisms in Ecosystems Consumers can be further divided into categories based on the things they eat and the way they obtain food. Primary consumers, or herbivores, eat plants as a source of food. Secondary consumers, or carnivores, are animals that eat other animals. Omnivores consume both plants and animals.

Keystone Species A keystone species plays a critical role in the maintenance of specific ecosystems. When bison are present in American tall grass prairie ecosystems, they increase the biodiversity of the site.

Energy Flow Through Ecosystems Each step in the flow of energy through an ecosystem is known as a trophic level. As energy moves from one trophic level to the next, most of the useful energy (90%) is lost as heat (second law of thermodynamics). Because it is difficult to measure the amount of energy contained in each trophic level, biomass (weight of living material) is often used as a proxy.

Trophic Levels in an Ecosystem

Energy Flow Through Ecosystems

Food Chains and Food Webs A food chain is a series of organisms occupying different trophic levels through which energy passes as a result of one organism consuming another. A food web is a series of multiple, overlapping food chains.

Food Web

Biogeochemical Cycles—Carbon Cycle Plants use carbon dioxide during photosynthesis to produce sugars. Oxygen is produced as a by-product. Herbivores eat plants, break down the complex organic molecules into simpler molecular building blocks, and incorporate those molecules into their structure. Respiration produces CO2 and water and releases those compounds back into the atmosphere.

Biogeochemical Cycles—Carbon Cycle The decay process of decomposers involves respiration and therefore recycles naturally occurring organic molecules. Carbon sinks are processes or situations that remove atoms from active, short-term nutrient cycles, such as sediments, oceans, and bodies of plants.

Carbon Cycle

Human Impact on the Carbon Cycle Burning fossil fuels takes carbon atoms that were removed temporarily from the active, short-term carbon cycle and reintroduces them into the active cycle. Converting forests (long-term carbon storage) to agricultural land (short-term carbon storage) has increased the amount of carbon dioxide in the atmosphere.

Carbon Sinks and Human Effects

Nitrogen Cycle The nitrogen cycle involves the cycling of nitrogen atoms between abiotic and biotic ecosystem components. Producers are unable to use atmospheric N. Must get nitrate (–NO3) or ammonia (NH3.) Nitrogen-fixing bacteria convert nitrogen gas N2 into ammonia. Decomposers also break down nitrogen-containing molecules, releasing ammonia.

Nitrogen Cycle Nitrifying bacteria are able to convert ammonia to nitrite, which can be converted to nitrate. Denitrifying bacteria are able (under anaerobic conditions) to covert nitrite to nitrogen gas (N2) which is ultimately released into the atmosphere. The primary sink for nitrogen is the atmosphere.

Nitrogen Cycle

Human Alteration of the Nitrogen Cycle If too much nitrogen or phosphorus is applied as fertilizer, or if it is applied at the wrong time, much of the fertilizer is carried into aquatic ecosystems. The presence of these nutrients increases the growth rate of bacteria, algae, and aquatic plants. Toxic algae can kill fish and poison humans. An increase in the number of plants and algae results in lowered oxygen concentrations, creating “dead zones.”

Phosphorus Cycle Phosphorus is not present in the atmosphere as a gas. The ultimate source of phosphorus atoms is rock. Phosphorus compounds are released by erosion and become dissolved in water. Plants use phosphorus to construct necessary molecules. Animals gain necessary phosphorus when they consume plants or other animals. Decomposers recycle phosphorus compounds back into the soil.

Phosphorus Cycle

Summary An organism’s environment can be divided into biotic (living) and abiotic (nonliving) components. The space an organism occupies is its habitat, and the role it plays is its niche. Organisms interact with one another in a variety of ways. Symbiotic relationships are those in which two species live in physical contact and at least one species derives benefit from the relationship. In an ecosystem, energy is trapped by producers and flows from producers through various trophic levels of consumers.

Summary The sequence of organisms through which energy flows is called a food chain. Multiple interconnecting food chains constitute a food web. The flow of atoms through an ecosystem involves all the organisms in a community. The carbon, nitrogen, and phosphorus cycles are examples of how these materials are cycled in ecosystems.